Generally, within the technical field of shock absorbers that include pilot valves, a pressure regulator, i.e. a valve arrangement, is used to control a flow of damping medium between a compression chamber and a rebound chamber during a reciprocal motion of a piston in a damping medium filled chamber of the shock absorber. The piston, via a piston rod, is connected either to a wheel or a chassis, whereas the chamber is connected to one of the wheel or chassis that the piston is not connected to. During a compression stroke the piston moves axially in a direction towards the compression chamber and thereby pressurizes the damping medium in the compression chamber. During a rebound stroke, the piston moves axially towards the rebound chamber, i.e. in the opposite direction, and thereby pressurizes the damping medium in the rebound chamber. In accordance with the function of the shock absorber, the pressurized damping medium needs to be transferred from the pressurized chamber to the other chamber, i.e. from the compression chamber to the rebound chamber or vice versa. The flow of damping medium needs to be controlled to obtain a damping effect of the piston and thus the shock absorber, i.e. to damp relative motion between the wheel and chassis.
The control of the pressure in the flow of damping medium in the shock absorber depends on the pressure created by the pilot valve. Pressure regulators in shock absorbers are usually provided with an axially movable or deflectable valve member, such as a washer, cone or shim that acts against a seat part. The pressure control is achieved by equilibrium or balance of forces, for example equilibrium between a pressure and/or flow force acting on the valve member in one direction and counteracting or opposing forces, such as one or more of a spring force, friction force or pilot pressure force acting on the valve member in the opposite direction. When the piston of the shock absorber moves at a certain speed such that the pressure and/or flow force become greater than the opposing or counteracting forces, the movable valve member is forced away from the seat part, thereby opening a flow passage. Thus, the movable valve member is forced to open at a stroke defined as a function of the flow produced by the pressure acting on the regulating area of the pressure regulator.
Traditional valve arrangements of the pressure regulating type described above generally have the disadvantage that the movable valve member opens abruptly when the piston of the shock absorber reaches a speed such that the pressure or flow forces become greater than the opposing forces. This may result in jerky or unsmooth damping performance, especially at low piston speeds.
In order to achieve smoother and more precise or accurate damping performance, especially at lower piston speeds, it is known to provide a bypass fluid flow passage bypassing the movable or deflectable valve member at low flows to achieve a less abrupt increase in damping effect with increasing piston or flow speed. One example of such an arrangement is disclosed in U.S. Pat. No. 5,934,421 where a spool valve arrangement is provided which, by moving the spool according to an electric current supplied to an actuator, directly and electrically adjusts or controls a flow path area of a bypass passage between the working chambers of the shock absorber and also adjusts a pilot pressure. The pilot pressure acts on the deflectable valve member and thus in turn controls the pressure regulating effect on a main flow. A disadvantage with the disclosed arrangement is that the bypass passage only allows relatively small flows to bypass the main flow. Consequently, the bypass fluid flow passage only has an effect at very low piston or flow speeds when the movable valve member is closed. Therefore, the disclosed arrangement only partially solves the problem of unsmooth and inaccurate damping performance at lower piston speeds.